Evaluation of Motor Vehicle Seatbelt Retractor Locking Devices

The seemingly never-ending increase in popularity of the more rollover-prone Sport Utility Vehicle type vehicles (SUVs) has provided an increased focus and urgency on rollover occupant protection. Field research has made clear that traditional, contemporary motor vehicle seatbelt retractors often fail to restrain occupants as expected. Various researchers have documented laboratory tests results and cited numerous real-world case studies describing these circumstances. These studies have typically focused on the response of the retractor’s inertial acceleration sensing lockup device. This device has been shown to allow surprising amounts of seatbelt spool out during long duration accident sequences with resulting multi-directional vehicle acceleration pulses such as those seen in typical rollover crashes. Further, increased injury potential has been discussed and attributed to such webbing spool out. One commonly implemented design countermeasure, or redundancy, to the retractor’s inertial sensor is a webbing velocity sensor intended to lock up the retractor independent of vehicle acceleration. This paper reports laboratory test data evaluating a wide spectrum of webbing velocity sensor designs found in current production vehicles. This study evaluates their relative performance, corresponding injury potential and occupant protection aspects of these designs.